Starting system for free-piston units



May 12, 1953 D. E. MEITZLER 2,638,266

STARTING SYSTEM FOR FREE-PISTON UNITS Filed June 11, 1947 4 Sheets-Sheet l ATTORNEY May 12, 1953 D. E. MEITZLER 2,538,266

STARTING SYSTEM FOR FREE-PISTON UNITS ATTORNEY Mayl 12, 1953 D. E. MElTzLr-:R 2,638,266

y STARTING SYSTEM FOR FREE-PISTON UNITS Filed June 11, 1947 4 Sheets-Sheet 5 F' Uf L SUPPLY PUMP ELECTRIC Pak/f# @LEA'D TYPE CHECK VALVE INVENTOR alzaldEM-'ZHII egpuc/M sneer/Na me .s1/PPL# vnLw: 2 4 ATTORNEY May 12, 1953 D. E. MEITZLER 2,638,266

' STARTING SYSTEM FOR FREE-KPISTON UNITS Filed June l1, `194'? 4 Sheets-Sheet 4 INVENTOR ganar/1E VZ ZE'IT' BY ATTORNEY Patented May 12, 1953 STARTING SYSTEM FOR FREE-PISTON x UNITS Donald E. Meitzler, Oak Ridge, Tenn., assignor to United Aircraft Corporation, East Hartford, Conn., a corporation of Delaware l Application June 11, 1947, Serial No. 753,945

, This invention relates to a starting system for afree-piston unit.

In the startingof free-piston units there is no structure by which the vunit can be motored since there is no crankshaft by rotation of which the 12 claims. (-01. 23o-56) pistons can be moved. Starting is accomplished by moving the opposed pistons rapidly together onthe compression stroke to cause ignition of the fuel in the lengine cylinder. A feature of the invention is an electrically controlled starting system by which to cause the rapid motion of the pistons. Another feature is the arrangement of the system such that only one operation of the starting system will occur each time that the system is put in operation.

A feature of the invention is a completely auy tomatic starting system that will go through one complete cycle before stopping.

In the co-pending appli-cation of Kunz, Serial No. '153,943 filed June 11, 1947, now PatentNo.

2,558,444, the compressor cylinders are single acty ing, and the inner ends of the cylinders are sealed to act as inverted air springs in controlling the frequency and length of stroke of the pistons.` A feature of this invention is the use vof vthe sealed compressor spaces for moving thepistons into starting position by applying pressure thereto during the starting operation. Another'feature is the automatic venting of these spaces to permit the pistons to be more easily moved together on .the starting stroke so that the pressurenormally existing in these springs is not effective during starting.

Other objects and advantages will be apparent from the specification and claims, and from the accompanying drawings which illustrate an em-k bodiment of the invention.

Fig. 1 is a sectional View through the free-piston unit showing the pressurized breatherand the starting valves. e

Fig. 2 is a sectional viewat a different angle through the unit to show the restraining linkage.

Fig. 3 is a diagrammatic View showing the operation of the starting system.

Fig. llis an enlarged view, in section, of the pressure valve.

The unit shown includes an engine cylinder I0 having reciprocating pistons I2 and I4 to which compressor pistons IB and I8 in cylinders 2|] and 22 areA integrally connected. Sleeves 244 and 26 attached to the compressor pistons complete the reciprocating piston assemblies.

engine compressionstroke. 1

,Ihe sleeves inV combination with stationary pistons 28 and 30 form air spring cylinders which serve to moveA the piston assemblies toward each other on the The piston assemblies are moved apart by burning fuel injected into the engine lcylinder by a fuel nozzle 32 operated by a fuel pump 34. Air compressed in the air spring cylinders on the power stroke returns the piston assemblies. 'I'he assemblies are always maintained at equal distances'from the center of the engine cylinder by a linkage which includes racks 36 extending from the compressor pistons and engaging a centrally located pinion 38.

Intake manifold 4U which may surround the compressor cylinders 20 and 22 conducts air to intake valves 42 at the outer ends of the compressor cylinders. The compressed air leaves the cylinders through discharge valves 44 also at the outer ends of the compressor cylinders and passes through scavenge manifold 46 to ports 48 in the engine cylinder which are uncovered by the piston I2 adjacent the end of the power stroke. When these ports are uncovered, air is blown through the engine cylinder and through exhaust ports l) which are uncovered by the piston I4 into the exhaust duct 5 I.

As shown in Fig. 1, the inner ends of the compressor cylinders 20 and 22 are interconnected by`a passagev 52 to form the pressurized'breather space. Pressure ismaintained in this space by means of a control valve 54, the function of which is to adjust the pressure in such a manner as to maintain the desired length of stroke for the pis-1 ton assemblies under normal operating condi- 5 6 sliding in a bore 58 `and normally closing a port 60 communicating with the breather spa-ce by a passage 62 and conduit 63. Bore 58 has another port 64 communicating by a passage `66 to a conduit 68 from the scavenge manifold 4,6. Plunger 56 is moved in a directionto connect ports and 64 to admit air from the scavenge manifold to the breather by a spring 'I0 acting onthe stem' 'I2 of the plunger, and by peak breather pressure in a chamber 'I4 acting on a diaphragm I6 also connected to the stem 12.

vAs shown, breather pressure in passage 62 acts on a checkvalve I8 in a connecting passage 80 between passage 62 and chamber 14. This check valve provides for the maintaining in chamber 141 of a" pressure close to the peak pressure in the breather. A small vent passage 82 bypasses the check valve for slowly bleeding olf the pressure in the chamber between successive compressor strokes. y

a passage 84 to a chamber 86 on the other side 0f the diaphragm.- The stem i2 also has mounted thereon another smaller diaphragm 8l forming another wall of chamber 86. On the other side of diaphragm 8l is atmospheric pressure in a chamber t vented as at 9i), one end of plunger 56 being in this chamber. As the pressure in the breather increases the pressure in chamber 'I- increases and moves plunger 56 downward to vent port Sil allowing a drop in pressure in the breather. Similarly a reduction in pressure in the breather causes a drop in pressure-in chamber 'M thus moving plunger 56 upwardly to connect ports 60 and t@ for admitting scavenge air to the breather.

The breather control may be made responsive to changes in altitude. To this end, stem i2 of the plunger is connected to a lever arm 92, one end of which engages with a sealed bellows.. 94.- which may be located in a vented chamber 06. The bellows may be acted upon by a spring 98 shown within the bellows. Asl the atmospheric pressure decreases, bellows Sf-'I- expands, thus moving plunger Sit downward tov decrease the pressure in the breather;

In addition to con-trolling the pressure in the breather during the operation of the unit, air under pressure may also be delivered to the breather space when the unit is not operating for the purpose of cranking the pistons into starting position. To this end, as shown in Fig. 3, air under pressure in a conduit from the starting air supply is delivered through a conduit |02 to the starting devices |04, and through aconduit |06 which connects with conduit 68. A pressure-reducing valve |00 is provided in the conduit |05 to reduce the pressure delivered through conduit |06 to the port 60 of: valve 54 and thence to the breather space.

The reducing valve Iiiii which maybe of any suitablel construction comprises, in the arrangement shown, a diaphragm I Hl; one side of which is vented as at II'2 to the atmosphere and' the other side of which is exposed to the pressure in the conduit Hit; The diaphragm is connected to a valve element IId which isy adapted' to close a passage I I'E for the air entering' the conduit' |06' and a spring IIS acting on the diaphragm normal-ly tends toA hold the valve element' H4 open. As the pressure builds up in the conduit |00',v the pressure on the diaphragm overcomes the action ot the spring |I8 and more or less closes the valve element |14, thereby maintaining` a limit on the pressure in the conduit |961 A solenoid valve I I9 in a control circuit opens the conduit IIiIiV to admi-t airV to the breather during the starting operation, as Will be pointed out, for the purpose of moving the pistons into the outer end positions shown.

i Aftery the pistons have been cranked' into the starting position of Fig. 1, they are movedv rap,- i'd-ly together by the starting devicesl |04. As shown, eachof these devices,` which may be Tocatedwithin thel airY spring pistons 28` and' 30, includes an accumulator chamber |'2'0 communieating with the air spring (the space |22) by a poppet` valve- |24. Thisv valve is connected toca` piston |26 by a piston rod t28 and is; normally held closed by a spring' |30 acting on the. piston. The cylinder |32 in which the piston I2'6` is slida.- ble communicates with the chamber so that. whenair under pressure is delivered to the chamber |20, the valve |24 will remain closed. As. shown, air under pressure reaches the, chamber F20 through the conduit |02` and a branch con.- duit It#` interconnects the opposed` starting. de-

vices at opposite ends of the unit so that both devices will be supplied with starting air` simultaneously.

After a predetermined air pressure has been built up in the accumulators |26 of the opposed starting devices, they are both vented simultaneously by delivering air under pressure through a conduit |36 connected with the starting air supply and communicating with the outer ends of the cylinders |32 in which the pistons |126 are positioned. By the application of air under pressure to these pistons, the valves |24 are opened rapidly and air from the chambers |20 enters the air springs and moves the piston, assemblies rapidly toward each other.

For unloading the breather during the operaation of the starting devices, after the pistons have been moved into starting position, the unit is provided with one or more unloading valves |38, each of which, as best shown in Fig. 1, iucludesa movable valve element iii-#|31 adapted to close ports |42 in the wall of the breather space 52. Each valve element |40 is connected by a rod' IM to a piston |46 inv a cylinder Int-8. The valve is normally urged into an open posi-tion by a spring I'Etv acting on the piston.

Air under pressure entering the outer end oi each cylinder |48 acts to move the valve |40 irl-to closed position against the action of the spring |561 The outer ends of the cylinders Il may beV connected by conduits |52- to the conduit |58 which, as above stated, communicates with the-conduit IilIV from the starting air supply. Thus, while pressure is being supplied through the conduit |06' to the space 52 for cranking the pistons to the outerends of the strokes inreadiness for starting, air pressure is simultaneously delivered to the cylinders |40 to hold the valves |40: closed. A check' valve |54 may beprovided in the conduit 68 to prevent the flow of air under pressure from the conduit |06 into and through the-conduit 68, thereby making it possible tobuild upy the necessary pressure tor ton unit is' provided by starting the motor |56i whicl'rdrives' the fuely supply'pump |50., This is accomplished by closing" a manually operated' switchv |60 on a control panel |621 This completes acontrol circuit through leads I64" to a relay |66 which, when energized, completes a.

power circuit from the power leadsy |568. and |10 through the relay operated switch |12. and leads |14. to. the motor |56'.

After the fuel supply motor is operating, the startingJ operation isY begun. by actuation of! a manual. push buttonv H5 which completes a circuit through one of the leads. |64 and a lead, |18 to a relay whichoperates aswitch. |82.. This. switch controls a. power circuit including, a normally closed switch |84 and a solenoid. |86 .which controlsthe valve. I I9 in the conduit |06. Thus, when. the switch |82. is4 closed, the. solenoid L36 is energized, to cause cranking air to enter the breather space and, acting on compressor pistons IIS and |,8fto move. the piston assemblies intothe positions of Fig. 1. As the pistons reach the outer ends of theirV stroke in. readiness for startinga cam |.90-l onY the pinion 38 Fig. 2:,.closes a switch |92 which completes a circuit. |94 through a relay |96 thatcontrols the switch |811.

ing devices.

The relay |96 opensl the switch |84 and.breaks the circuit through the solenoid |86 thereby cutting off any further air supply tothe breather space and, by reducing the pressure in,k cylinders |48, ventingv the breather space. l

The circuit |94 also includes the solenoid |98 that controls a valve 200 in the conduit |02 which supplies starting air under pressure to the start- Thus, when the solenoid |98 is energized, starting air is delivered to the starting devices to build up the desired pressure in the chambers |20.

The circuit through the solenoid |98 is controlled by a switch 202 actuated by a relay 204. This relay and another relay 206 are controlled by the contact bar 208 of a pressure switch 209 which is moved in response to pressure in a bellows 2|| connected to the conduit |02. The bai` 208 normally completes a circuit through the solenoid |98. As the pressure is built up in conduit |02, this circuit through solenoid |98 is broken and a circuit 2|0 through the relay 204 is completed to open the switch 202. The contact baralso completes another circuit through the relayk 206 which operates a switch 2|4 to complete a circuit through asolenoid 2|6 which operates a valve 2|8 in the conduit|36 to admit air under pressure to the cylinders |32 foropening valves |24. Thus, when the pressure in the chambers |20 has reached the predetermined value, the air in these chambers is released by the operation of the valve 2|8, thereby causing the pistons to be moved rapidly toward each other` on the starting stroke. When the switch 2|4 is moved to close the circuit through the solenoid 2 6, it breaks a `circuit through a solenoid 220 which controls a normally open valve 222 on a vent conduit 224 from the conduit |36. The starting system having functioned, the push button |16 is released and the parts arel restored to the positions shown in readiness for restarting the unit.

In operation the free-piston unit while running has the breather space 52 sealed by the valves |40 so that'this space acts as an inverted air cushion. The maximum pressure in this breather space is adjusted as a function of the scavenge pressure by the action of the diaphragm 16 which is exposed to scavenge air pressure in the chamber 86. V'Ihus, as scavenge pressure increases, the plunger 56 is moved upward, Fig. 3,y to admit scavenge air through the conduit 63 to the breather space.

When the pistons approach the inner ends of their strokes, the pressure in the breather is suflicient to cause the check valve 18 to open and admit pressure to the chamber 14 so that the pressure of the scavenge air in chamber 86 is balanced by the breather air 'pressure in chamber 14' andthe spring 10. In addition to adjusting the breather pressure as a function of scavenge pressure, it may also be adjusted as a function of atmospheric pressure through the function of the sealed bellows 94 which expands as the atmospheric pressure decreases to movey the plunger 56 downward and vent the breather space through the passage 63. y

Assuming now, that the unit has been stopped and is to be started, the switch |60 is closed to start the fuel supply Ypump |58 thereby assuring the necessary fuel for the injection pump 32. The push button |16 is thenheld down to cause the starting operation. Thev rst step in the operation is the opening of `the solenoid valve ||9 which admits air to the cylinders |48 for-holding the vent valves closed and also admits start ing air through the conduits 68 and past plunger 56 to the breather space 52. Itwill be apparent that as the high starting air pressure reaches conduit 68, it also enters chamber 86 thereby moving the plunger 56 upward, Fig. 4, to interconnect ports andr64. Pressure inthe breather will cause outward movement of the pistons into the starting position of Figs. 1 and 2. When the pistons reach starting position, the cam |90 closes switch |92which opens the solenoid valve 200 for charging the starting devices |04. This same switch operates the relay switch |84 t0 cause the solenoid valve 9 to be closed` and permit the air pressure in the breather space to vent through the bypass |55 into the scavenge system.

When the pressure in the starting devices reaches a predetermined value, the contact bar 208 of the pressureswitch completesV a circuit which opens the solenoid valve |98 thereby admitting air under pressure to the outer ends of the cylinders |32 thereby opening the valves |24 to admit air under high pressure to venter the air springs |22 and move the pistons rapidly together. Obviously when the cylinders |48 have been vented byl closing of the valve I9, the vent valves |40 are opened by the springs |50 so that when the starting devices operate for moving the pistons vrapidly together, the breather space is connected with the inlet manifold so that there is no pressure acting on the inner side of the compressor'pistons. When the unit is operating, push button |16 is released thereby restoring the starting system to its original position in readiness for a subsequent starting operation. y

The pressurized breather together with the valves |40 for the purpose of venting the breather duringthe starting operation and the mechanism by which to maintain the desired pressure within the 'breather is an invention of Kunz claimed in hisvco-pending application, Serial No. '753,943 led June 11, 1947, now Patent No. 2,558,444.

It is to be understood that the invention is not limited to the specic embodiment herein illustrated and described, but may be used in other ways without departure from its spirit as defined by the following claims.

I claim:

1. A starting system for a free-piston unit, said unit including an engine cylinder and piston, a compressor cylinder and piston, said cylinders being connected together and said pistons being connected together to form a reciprocating piston assembly, fan air spring including cylinder `and piston parts one of which is connected to the piston assembly and the other of which is connected to the engine and compressor cyl-` inders, said compressor cylinder having inlet and discharge valves at one end for controlling the flow of gas into 4and out of said one end of the compressor cylinder, means for closing the other end of the cylinder to form a pressurized space, and valve means communicating with said other end ofthe cylinder for venting said space, said starting system including an accumulator for gas lunder pressure with means for admitting gas to said accumulator, means including a fluid connection between said accumulator and the air spring cylinder and a valve in said connection for venting said accumulator into the air spring for moving the `piston -assembly on the starting stroke, means for admitting gas under pressure lto said pressurized space for moving the piston assemblyxto the outer end of its power stroke aeeaaee 9" said port, means connected to said other end ofthe compressor cylinder for admitting fluid under pressure to said other end of said compressor cylinder for moving the pistons to starting position, means connected to said venting means and responsive to pressure inrsaid manifold for closing the venting means for said other end of said cylinder, and means for causing said cylinder venting means to open When the pistons reach starting position for venting the' cylinder during the operation of the starting system.

7. 'Ihe combination With a free-piston unit including an engine cylinder having opposed pistons therein, a compressor cylinder attached at each end of the engine cylinder, a compressor piston in each compressor cylinder, each of said engine pistons and the adjacent compressor piston being interconnected to move as a unitary piston assembly, an air spring associated with each piston assembly and including cylinder and piston members, one of which forms a part of' the piston assembly and the other of which is stationary, each of said compressor cylinders having inlet and discharge valves at one end thereof, means for closing the other ends of the compressor cylinders, and duct means interconnecting said other ends to define a pressurized space, of a starting system including valve means communicating with said pressurized space for venting saidpressurized space, pressure responsive means connected to said Valve means for holding said valve means closed, means for delivering uid under pressure to said space and also to said pressure responsive means for causing the piston assemblies to be moved into starting position, an accumulator chamber for gas under pressure, means for supplying gas to said accumulator, a port providing a communication from said chamber to one of the air springs, and a valve controlling said port, fluid pressure actuated means connected to said port controlling valve for moving said port controlling valve into open position, means responsive to the motion of the piston assembly into starting position for discontinuing the supply of fluid under pressure to said pressurized space and also tothe pressure responsive means by which to hold the space venting valve means closed, and 'means having uid connection with the accumulator chamber and responsive to pressure in the accumulator chamber for supplying uid under pressure to the pressure actuated means for the port controlling valve thereby to open said last valve.

8. A starting system for a free-piston unit, said unit including an engine cylinder and piston, a compressor cylinder and piston, said cylinders being connected together and said pistons being connected together to form a reciprocating piston assembly, an air spring cylinder member and piston member, one of said members being connected to and moving with the piston assembly, said compressor cylinder having inlet and discharge valves at one end for controlling the flow of gas into and out of said one end rof the compressor cylinder, means for closing the other end of the compressor cylinder to form a pressurized space, and valve means communicating with said space for venting it, said starting system including an accumulator for gas under pressure with means for supplying gas to said chamber, means including a fluid connection between said accumulator and the air spring cylinder and a valve in said connection for venting said accumulator into the air spring cylinder for moving the piston assembly on the starting stroke, means communicating with said space forA admitting gas under pressure to said space for moving the piston assembly to the outer `end of its poWer stroke prior to the operation of the accumulator venting means, and pressure responsive means connected to the space-venting means for holding said space-venting means closed during the admission of gas under pressure to said space.

` 9. A free-piston unit including an engine cylinder and piston, a compressor cylinder and piston, said cylinders being connected together and said pistons being connected together to move as a unit, an air spring including cylinder and piston parts one of which is connected to the piston assembly and the other of which is connected to the engine and compressor cylinders, saidl compressor cylinder having inlet and discharge valves at one end for controlling the flow of gas through said one end of said compressor cylinder, and means communicating with the other end ,for maintaining a predetermined pressure in said kother end of said compressor cylinder, in combination with a starting system for said unit including an accumulator chamber for gas under pressure with means for supplying gasl to said chamber, a port in said accumulator cham-` ber communicating with said air spring, a valve controlling said port, pressure responsive means connected to said valve for moving said valve into. open position for causing discharge of gas under pressure through said port and into said air` l0. A free-piston unit including an engine cylinder and piston, a compressor cylinder and piston, said cylinders being connected together and said pistons being connected together to move as a unit, an air spring including cylinder and piston parts one of which is connected to the piston assembly and the other of which is connected to the engine and compressor cylinders, said compressor cylinder having inlet and discharge valves at one end for controlling the flow of gas through said one end of said compressor cylinder, and means communicating With the other end for maintaining a predetermined pressure in said other end of said compressor cylinder, in combination with a starting system for said unit including an accumulator chamber for gas under pressure with means for supplying gas to said chamber, a port in said -accumulator chamber communicating With said air spring, a valve controlling said port and movable into open position for causing discharge of gas under pressure through said port and into said air spring for moving the pistons on the starting stroke, means for admitting fluid under pressure to the other end of said compressor cylinder for moving said pistons into starting position, means responsive to the pressure in said chamber for causing the valve for said chamber to open, and pressure actuated valve means for venting said other end of the compressor cylinder during the time that the port controlling valve is open.

11. A free-piston unit including an engine cylinder and piston, a compressor cylinder and piston, said cylinders being .connected together and said pistons being connected together to move as a unit, .an airspring including cylinder and piston parts one of which is connected to thepiston .assembly and the other of which is connected to the engine .and compressor cylinders, said compressor cylinder having inlet and discharge valves at `one end for controlling .the flow of gas through said one end of said compressor cylinder, means communicating with the other end for maintaining apredetermined pressure in said other end of said compressor cylinder, in combination with a starting system Vfor said unit including an accumulator chamber for gas under pressure with means .for supplying gas to said chamber., a port in said accumulator chamber communicating With said air spring, a valve controlling said port and movable 'into open position for causing discharge of gas und-er pressure through .said port and into said air spring for moving the pistons on the starting stroke, means for admitting fluid under pressure to vthe other end ci said compressor cylinder .for moving said pistons into starting position, and `means responsive .to movement of the pistons into starting position for rdiscontinuing the supply .oi lfluid under pressure to said other end of said compressor cylinder and for venting vsaid other end of said compressor cylinder.

12. A free-piston unit including an engine cylinder and piston, a compressor cylinder and piston, said cylinders being connected. together and said pistons being connected together to move as a unit, an air spring including cylinder and piston v parts .one of which is connected to the piston assembly and the other of which is connected to the engine and compressor cylinders, said compressor cylinder 'having inlet and discharge valves at one end for controlling the iiow of gas through said one end of saidcompressor cylinder, .means communicating with the other end for maintaining a predetermined pressure in said other end of said compressor cylinder, and means for venting said other end of said compresser cylinder `including a pressure-operated valve closing a port communicating with said other end of the cylinder, in combination with a starting system including .an accumulator vchamber `for gas under pressure, said chamber having a port therein communicating with said air spring, a valve controlling said port and movable into open ,position for causing discharge of gas under pressure from said chamber through the port into said air spring for moving the pistons on the starting stroke, means for charging said chamber with gas under pressure, means responsive "to the .pressure in said chamber for operating said valve, and a vent connection from said pressure-operated valve for causing said valve to be open during the `operation of said chamber-venting valve.

- DONALD E. MEITZLER.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 2,165,328 Pescara Aug. 8, 1939 2,344,058 Pescara 'Mar'. 14, 1944 2,434,280 Morain Jan. 13, 1948 y2,434,877 TWelsh ret al June 20, 1948 2,558,444 Kunz June 26, 1951 FOREIGN PATENTS Number Country Date 541,7 19 Great Britain Deo. 11, 1941 

